n-alkanes has a number of industrial applications as it can be used as feedstock for manufacture of numerous intermediates and finished products, such as alcohols and ketones, having tremendous demand in the manufacture of variety of industrially important products. The alcohols and ketones are either sulfonated or ethoxylated to different types of detergents. Fatty alcohols and their derivatives are of great commercial importance as surfactants, plasticizers, etc. The most widely used are C12-C16 fatty alcohols. In the literature, a number of studies have been reported on the oxidations of higher alkanes to alcohols and ketones via air or oxygen as an oxidant. Reactions of alkanes with alkyl hydroperoxide for the manufacture of alcohols and ketones have also been extensively studied in the literature. But there are no reports on the production of a mixture of alcohols and ketones by liquid phase oxidation of isopentane to alkyl hydroperoxide with simultaneous transfer of oxygen to alkanes.
The uses of palladium metal and palladium organometallic complexes for alkane oxidation are well known. A majority of literature reports on palladium catalyzed oxidation deal with lower alkane oxidation ranging from methane to butane using molecular oxygen, in a highly acidic medium. References may be made to the paper, Metallokompleksnyi Katal., 116-29, 1977 by Rudakov et al. wherein the oxidation of saturated hydrocarbons is reported using palladium (II) complexes as catalysts in highly acidic media like sulfuric acid, sulfuric acid-aluminum sulfate, and phosphoric acid-boron trifluoride. The disadvantage of this system is the essential requirement of a highly acidic medium, to conduct the reaction, which is avoided in the present invention. The present invention can be conducted without any solvent, and hence is avoid of any acidic/corrosive components.
References may be made to another paper, New J. Chem., 13(10-11), 761-6, 1989, by Herron et al., wherein zeolite supported Fe/Pd bimetallic catalysts are used for the selective oxidation of alkanes at room temperature. Here a mixture of hydrogen and oxygen, or H2O2 is used as an oxidant.
U.S. Pat. No. 5,235,117 teaches the preparation of boric acid and its use in the oxidation of saturated hydrocarbons to alcohols is reported. In the present invention the oxidation catalyst used is supported Pd catalyst, which catalyzes the alkane oxidation in the presence of alkyl hydroperoxide. No boric acid is employed in the present invention.
PdSO4.2H2O is used as a catalyst in International Patent Appl. WO 9214738 A1 to convert methane to MeOSO3H in 20% oleum at 100° C. The process uses PdSO4 as an oxidation catalyst for oxidation of methane to esters and alcohols in highly acidic medium is also reported. In the present invention, the catalyst used is a supported Pd catalyst and the reaction is carried out in a solvent, free from any acidic components.
A very high alcohol to ketone ratio was reported in the oxidation of cyclohexane with t-butyl hydroperoxide (TBHP) over Fe-tris[2-pyridyl methyl]amine catalyst. The alcohol: ketone ratio was 18, at an alkane conversion of ˜30% [J. Kim et. al. J. Mol. Catal. A:Chem., 117, 83, (1997)]. The oxidation of cyclohexane by TBHP in the presence of titanium alkoxide produced the corresponding alcohols and ketones, whereas, other titanium complexes with titanyl or peroxo-titanium groups were not effective [(M Fujiwara et al., J. Mol. Catal. A:Chem., 142, 77 (1999)].
Metal porphyrin catalysts are also reported to be active for the oxidation of isobutane and cumene. In the presence of oxygen these substrates form the hydroperoxide, which then decomposes to yield the alcohol and ketone. The oxidation of n-dodecane with cumene hydroperoxide or TBHP to detergent grade alcohols has been reported using Fe, Mn, Co porphyrin catalysts and mixtures [U.S. Pat. No. 4,978,799 (1990)]. Metal acetylacetonate complexes are reported to be active for the oxidation of isobutane and cumene. In the presence of oxygen these substrates form the hydroperoxide, which then decomposes to yield the alcohol/ketone products. The productions of detergent grade alcohols by the oxidation of n-dodecane with cumene hydroperoxide or TBHP have been reported using Fe, Ru and Cr acetyacetonate catalysts and their mixture [U.S. Pat. No. 4,978,800 (1990)]. In the presence of RuCl2(PPh3)3, and TBHP, decane oxidation with 28% conversion has been observed. Ketones are the major product formed with 38% selectivity. The alcohol formation is about 2% [S. I. Murahashi, et al., Tetrahedron Lett., 34(8), 1299 (1993)]. U.S. Pat. No. 4,459,427 (1984) describes a process for the production of alcohol and ketone derivatives by reacting the linear or branched alkanes (C2-C20) with TBHP at ambient or elevated temperature and pressure in the presence of iron or manganese phthalocynine or porphyrin square planar complexes having heterocyclic nitrogen donor ligands, and where the complex has either no axial ligands, e.g. the lower valency or cationic complex, or has an axial ligand which is non-coordinating or weakly-coordinating. D. Mansuy et al. [Angew. Chem. Intl. Ed. Engl., 19 (11), 909 (1980)], describe the hydroxylation of cyclohexane and n-heptane by alkyl hydroperoxide using metalloporphyrin and in particular iron (111) and manganese (111) porphyrins in the form of Fe(tetraphenyl porphyrin)Cl and Mn(TPP)Cl. Ru/C has been used for the oxidation of different alkanes (cycloalkanes, n-heptane and n-decane) using TBHP and peracetic acid as the oxidants, to yield 72-90% of oxygenates (alcohol+ketones) [S. Murahashi, et al., J. Org. Chem., 65, 9186 (2000)].
The oxidation of cyclohexane, hexane and heptane to alcohols and ketones has also been reported using cis-[Ru(II)(L)2—(OH2)2]2+ complex catalysts (where L=substituted 2,2′-bipyridines of 1,10-phenanthrolines [T. Lau et al., J. Chem. Soc., Chem. Commun., 1406 (1988)].
Numerous heterogeneous catalysts have also been found to be active for the oxidation of alkanes. Co/Mn supported on different microporous aluminophosphates were used for the oxidation of dodecane with air at 100° C. [R. Raja and J. M. Thomas, Chem. Commun., (17), 1841 (1998)]. The highest conversion of dodecane reported was 5.5%. The products formed were C12 alcohols, ketones and gaseous carbon oxides. The selectivity to alcohol and ketone was 35% and 20%, respectively. The selectivity for terminal alcohol and aldehyde was 37%.
In the literature, a number of researchers have reported that the detergent grade alcohols were obtained in high selectivity by the oxidation of higher alkanes using boric acid as a catalyst. A. N. Bashikirov, et al. [Proc. World Pet. Cong., Vol. 4 175 (1959)] have reported the synthesis of higher aliphatic alcohols by liquid phase oxidation of paraffinic hydrocarbons in the presence of boric acid and found that a high selectivity to alcohols can be achieved by proper selection of reaction conditions. Nippon Shokubai in Japan practices a commercial process for the manufacture of detergent alcohols by alkane oxidation in the presence of boric acid [U.S. Pat. No. 3,660,504 (1972)]. Here the diluted oxygen (5% in nitrogen) is used as the oxygen source and the alkyl hydroperoxides are formed in situ. These interact with the boric acid to form borate esters, which on hydrolysis yield the detergent alcohols. The conversion level for alkane is 31% with a selectivity of 72% to alcohols. No metal catalysts are used in this process. The boric acid serves as an esterification agent in the oxidation, which prevents them from further oxidation by interrupting the oxidative conversion chain at the alcohol stage. A similar observation has been reported by N. J. Stevens and J. R. Livingston “A New Route for Alcohols” [Chem. Eng. Progress, 64(7), 62 (1968)]. M. Iam and M. Hassan [(Ind. Eng. Chem. Prod. Res., 20, 315 (1981)] have reported that the direct oxidation of n-dodecane in the presence of boron compounds like tributoxyboroxine, boron trioxide, dibutoxyborane, etc. using dilute oxygen (4% O2 in N2) leads to a mixture of the six possible straight-chain C12 alcohols.
U.S. Pat. No. 5,767,320 (Raja and Ratnasamy, 1998] describes a process for the oxidation of cyclohexane to a mixture of cyclohexanone and cyclohexanol using Fe, Co, Cu, Cr, Mn complex of phthalocynine or porphyrin and mixture as catalysts in which some or all of the hydrogen atoms of the phthalocynine or porphyrin have been replaced by electron withdrawing groups.
The above literature reveal that the production of alcohols and ketones by the oxidation of alkanes using homogeneous porphyrin, phthalocynine and similar planar complexes of metal like Fe, Co, Mn, Cu, Ru, Rh and supported catalysts in the presence of alkyl hydroperoxide [TBHP, CHP]. In the literature, there are no reports available on the co-oxidation involving alkanes and isoalkanes in presence of oxygen for the preparation of alcohols and ketones.
In the present invention provides a process for the preparation of a mixture of alcohols and ketones by liquid phase oxidation of isoalkanes to alkyl hydroperoxides with simultaneous transfer of oxygen to alkanes in presence of heterogeneous catalysts.
This invention provides a process by the use of a heterogeneous catalyst system, which can be separated from the reaction mixture with ease and reused for another reaction and also provides a process that is environmentally more benign.